Of course, I'm saying that when I have a story that I'll have finished soon (hopefully not too much later than soon) that might just be one of the best handling of time travel in Sailor Moon since ever. And that's coming from a person who is normally self-deprecating. @_@

To get more on topic, if it's a serious story then I think the limit regarding the amount of series being crossed over with would be defined by how many of said series' settings and mechanics don't come into conflict with any among themselves. Unless you're fusing the series together, of course: in which case that's another matter entirely.

The part about Pluto and the Door of Time (AKA the Time Gate) sounds like fanon, anyway. The Door of Time is simply used to be traveled through, not as any kind of spying device or having the capability to purview the "timeline," alternate universes or whatever. The problem begins as soon as you assign her with more power, ability or resources than she actually has, because power over time is a slippery slope in terms of abuse. In reality, "limiting" the kind of Pluto you're talking about is actually taking her back in the direction of being what's supposed to be normal, rather than abnormal.

The other solution is parallel worlds, and/or a new worldline branching off for each significant event. Read H. Beam Piper's Paratime stories. The best is Lord Kalvan of Otherwhen, but it's not nearly as educational in this respect. I've seen this one used on Pluto quite a few times -- there's even a peculiar location outside of time where the Plutos get together every now and then to compare notes.

Spica75 wrote:Mmm, although potentially very useful for fiction, i really never liked the parallel/branching worlds variant, for the simple reason that it breaks the most fundamental law of physics, something created out of nothing.

There´s also the problem of WHO determines what is a significant event? If an ant has the option of turning left, right or go straight, is that significant? It certainly could be, but you can´t know that before you actually see the results. Which means we either have a smart universe, or one that predicts the future.

We don't know enough about the Big Bang (or its alternatives) to know how our universe was created. For all we know, we're just a zero-point fluctuation in some larger universe. Something can be created out of nothing, as long as it goes away again before the Universe notices. That's just another formulation of the uncertainty principle.

The many-worlds interpretation of quantum mechanics says that any quantum effect is significant. There are a lot of universes, and more coming into being each moment. Most quantum effects won't make a big difference, so you'd have something like a continuum as you moved sideways in time. If you notice a difference as you moved, that was caused by a significant event. "Significant" in this case would be defined in the same way as "great" when applied to men, women, events, or art -- you wait a few centuries and see what people think.

Spica75 wrote:AFAIK, that principle is about the limit to what extent we can know where or in what state something is, not that particles can appear out of nothing. It´s a huge difference between "we cant measure all particles or energies" and "particles and energies can appear out of nothing".

The creation of virtual particles out of nothing cannot be observed -- but the consequences can, at least in theory. In most cases, you'll get a particle/antiparticle pair. Normally they would recombine, but under extraordinary circumstances they may not. That's one explanation of Hawking radiation: a particle/antiparticle pair appears near the event horizon of a black hole, and the black hole gulps up one of the pair. That leaves the other particle wandering about, scratching its head and wondering where its soulmate is. The result is radiation. Now I admit, I'm neither a particle physicist nor a cosmologist -- but there are enough of them saying this kind of thing.

Spica75 wrote:Why would they appear?

Never ask a physicist "why". The best you'll get is a nested series of "how" that ends up in a different "why".

Spica75 wrote:Like timetravel, it´s a very popular concept to play around with(especially in fiction), but the reasoning behind always seems to fall apart when looked at.

If the reasoning falls apart, get some glue and put it back together any way you like.

Spica75 wrote:I´ll admit that unlike timetravel, there is a tiny chance that the universe is really a multiverse of one sort or another, but the more i went over it, the more unlikely i found it. To the point where I consider the probability negligable at most.

String theory predicts extra dimensions. We're familiar with our three spatial dimensions, and then there's the time dimension. That makes four. I've seen theories with ten dimensions on up. If those dimensions exist, who knows what they're doing? Perhaps that's where paratime is hiding!

But it all comes down to this: nobody has really proven the multiverse, extra dimensions and all, exists. So if the full set of rules is unknown, do what makes your story work. Because if you're playing with anime, and especially Sailor Pluto, the material universe is only a suggestion.